Until recently, the Cathode Ray Tube ("CRT") has been the primary device for displaying information. While having sufficient display characteristics with respect to color, brightness, contrast and resolution, CRTs are relatively bulky and power hungry. These failings, in view of the advent of portable laptop computers, has intensified demand for a display technology which is lightweight, compact, and power efficient.
One available technology are flat panel displays, and more particularly, Liquid Crystal Display ("LCD") devices. LCDs are currently used for laptop computers. However, these LCD devices provide poor contrast in comparison to CRT technology. Further, LCDs offer only a limited angular display range. Moreover, color LCD devices consume power at rates incompatible with extended battery operation. In addition, a color LCD type screen tends to be far more costly than an equivalent CRT.
In light of these shortcomings, there have been several developments recently in thin film, Field Emission Display ("FED") technology. In U.S. Pat. No. 5,210,472, commonly assigned with the present invention, and incorporated herein by reference, a FED design is disclosed which utilizes a matrix-addressable array of pointed, thin-film, cold emission cathodes in combination with a phosphor luminescent screen. Here, the FED incorporates a column signal to activate a single conductive strip within the cathode grid, while a row signal activates a conductive strip within the emitter base electrode. At the intersection of both an activated column and an activated row, a grid-to-emitter voltage differential exists sufficient to induce a field emission, thereby causing illumination of the associated phosphor of a pixel on the phosphorescent screen. Extensive research has recently made the manufacture of an inexpensive, low power, high resolution, high contrast, full color FED a more feasible alternative to LCDs.
In order to achieve the advantages of this technology, as in the performance of LCDs, FED devices require a gray scale range control scheme. Several techniques have been proposed to control the brightness and gray scale range. For example, inventor Dunham in U.S. Pat. No. 5,103,144, and inventor Doran in U.S. Pat. No. 5,103,145, both incorporated herein by reference, teach methods for controlling the brightness and luminance of flat panel displays. However, there remains a need for a gray scale range control scheme that requires less power, is simpler to manufacture. Further, a need exists for a gray scale control scheme requiring less circuitry and thus less surface area on a silicon die.